1. Field of the Invention
The present invention relates to multicarrier signal receivers, and more particularly, to receivers for compensating nonlinearly distorted multicarrier signals.
2. Description of the Related Art
In wireless telecommunications as defined in IEEE 802.11 standard protocols, information is transmitted and received by using multicarrier signals such as orthogonal frequency division multiplexer (OFDM) signals. The wireless telecommunications using these OFDM signals include wireless local area network (LAN), European digital terrestrial video broadcasting (DVB-T), and the like.
FIG. 1 is a block diagram of an ordinary multicarrier signal transmission and reception system for wireless telecommunications. Referring to FIG. 1, a transmitter 1 of an ordinary multicarrier signal transmission and reception system for wireless telecommunications has a forward error correction (FEC) encoder 3, a mapping unit 4, a pilot insertion unit 5, an inverse fast Fourier transform (IFFT) unit 6, a guard interval (GI) insertion unit 7, a digital-to-analog (DA) conversion unit 8, and an up-converter 9. In addition, the transmitter 1 has a nonlinear high power amplifier (HPA) 10 which performs high power amplification for the output signal of the up-converter 9 and transmits to the air. The signal transmitted to the air is transmitted through a multipath channel 11 and is received by a receiver 2. The receiver 2 has a down-converter 12, an analog-to-digital (AD) conversion unit 13, a GI removal unit 14, a demodulation unit 15, which is formed with a fast Fourier transform (FFT) unit 16 and an equalizer 17, a demapping unit 18 and an FEC decoder 19.
However, in this multicarrier signal transmission and reception system, due to the use of the nonlinear HPA 10, in-band nonlinear distortion is caused such that the symbol error rate (SER) is degraded. In order to reduce this nonlinear distortion, such techniques as a back-off scheme, clipping, a peak-to-average power reduction scheme, a pre-distortion technique, and a special type of error correction, are being used. A drawback is that these techniques to reduce nonlinear distortion should also be implemented in the transmitter 1 to modify the conventional standard transmission protocol.
FIG. 2 shows a method for reducing nonlinear distortion, known as a decision-aided reconstruction (DAR) technique. The technique is described in an article by D. Kim, L. Stuber, “Clipping noise mitigation for OFDM by decision-aided reconstruction”, IEEE Commun. Letters, Vol.3, No. 1, January 1999. Referring to FIG. 2, the DAR receiver for receiving a nonlinearly distorted multicarrier signal has an FFT unit 20, an equalizer 21, a decoder 22, an IFFT unit 23, an up-sampler 24, a nonlinear transfer function output unit 25, a down-sampler 26, and an FFT unit 27.
However, a drawback is that the DAR receiver in FIG. 2 should know the nonlinear transfer function g(.) in advance. In order to estimate the function g(.) when the nonlinear transfer function g(.) is not known, a method may be used in which, when a signal is transmitted, side information or a special training signal that is needed for reconstruction of g(.) is transmitted together. This method reduces throughput of the telecommunications system and at the same time should modify the existing standard transmission protocol. Accordingly, it is difficult to apply this method to a telecommunications system using a multicarrier signal, such as an OFDM signal.